The present invention generally relates to gas flow control valves, and more particularly to gas valves installed in gas supply lines to stop the flow of gas in the event of a leak in the supply line.
Gas-fired appliances using fuels such as methane, butane, propane, or combinations thereof are commonly used throughout the world. Although such appliances and the systems that supply fuel to them are well-developed and thoroughly engineered, there exists a small but significant chance for a malfunction to cause a catastrophic accident. Gas leaks in the appliance or the supply system can and do cause deadly fires and explosions every year. Many of these incidents could be prevented through greater exercise of caution and vigilance, while other accidents caused by mechanical failure, broken supply pipes, and the like could be prevented by the use of gas leak sensor shutoff valves. However, gas leak sensor shutoff valves are not in widespread use.
In populous areas of the world where geological fault lines are known and seismic events are common, it is recognized that gas supply lines are very vulnerable to earth tremors and shifting. It is also known that the major destructive effect of many earthquakes has been firestorms caused by the abundance of fuel leaking from broken gas pipes and the related lack of water supply for extinguishing fires. Again, gas leak sensor shutoff valves could ameliorate this potential for catastrophe, but such valves are not in widespread use. Seismic sensor valves, which shut off gas flow in response to a seismic event, have been installed in a few buildings, and their use has been generally unsuccessful. Seismic events may trigger the valve to stop the gas flow, even though the gas system is undamaged and remains intact. As a result, the gas system is interrupted and rendered inoperative for no valid reason. Moreover, seismic sensor valves may be triggered by non-seismic vibrations, such as sonic booms, shaking caused by the near passage of very heavy vehicles, and the like. It is then necessary to relight all pilot flames, and to reset the associated pilot valves. Most homeowners and building dwellers cannot carry out these tasks themselves, and must pay a skilled tradesman for the service.
Seismic sensing valves tend to be expensive, due to design complexity, and the cost itself is a negative incentive for widespread use. In addition, seismic sensing valves are generally installed by being secured to a wall of the building or dwelling being protected, and the valve must be precisely leveled to be effective. The gas piping must then be routed through the valve, and the added pipe and connectors, as well as the labor for the wall installation, leveling, and pipe make-up comprise a significant additional cost factor. It is not surprising, considering the false triggering problems and the high cost, that seismic sensing valves are not widely used.
Gas leak sensor shutoff valves are known in the prior art, as exemplified in Israel patent no. 96312, issued to the present inventor. Such devices are effective in distinguishing between nominal gas flow for appliance use and exceptionally high gas flow due to a leak in the gas supply system or gas-fired appliance. Such devices could be more widely exploited if they are made to be as simple, effective, and inexpensive as possible.